Threading machine having spindle feed means and spindle return means



Nov. 13, 1956 c. H. LAEMMEL 2,769,991 THREADING MACH INE HAVING SPINDLEFEED MEANS AND SPINDLE RETURN MEANS Filed Nov. 18. 1952 4 Sheets-Sheet lA 72 INVENTOR. T x B 6% W 2 y I Nov. 13, 1956 c. H. LAEMMEL 2,769,991

THREADING MACHINE HAVING SPINDLE FEED MEANS AND SPINDLE RETURN MEANS 4Sheets-Sheet 2 Filed NOV. 18, 1952 INVENTOR.

Nov. 13, 1956 H LAEMMEL 2,769,991

C. THREADING MACHINE HAVlNG SPINDLE FEED MEANS AND SPINDLE RETURN MEANSFiled Nov. 18, 1952 4 Sheets-Sheet 3 INVENTOR.

E2 @ZM W Patented Nov. 13, 1956 THREADING MACHINE HAVING SPINDLE FEEDMEANS AND SPINDLE RETURN MEANS Charles H. Laemmel, Dayton,

Sheifield Corporation, Ohio Ohio, assignor to The Dayton, Ohio, acorporation of This invention relates to threading apparatus.

One object of the invention is the provision of a unitary threading unitfor use with a workpiece holder, and of compact and rugged constructionand which is simple and accurate in its operation.

Another object of the invention is the provision of a threading unit ofthe character referred to which can perform completely automaticthreading operations or which can be readily adapted to manual control.

Another object of the invention is the provision of a threading unit ofthe character referred to which has a positive lead control for spindleadvance upon rotation by a drive means and which includes a controllablyoperable return drive.

Another object of the invention is the provision of a positive leadcontrol which includes a lead screw on the tool carrying spindleassociated with a controllable lead nut means.

Another object of the invention is the provision of a positive leadcontrol of the character referred to which is readily accessible andwhich is quickly removable for insertion of lead control components.

Other objects and advantages of the invention will be apparent from thefollowing description, the appended claims, and the accompanyingdrawings, in which,

Figure l is an overall perspective view showing a threading unitembodying the present invention associated with a workpiece holder and aplatform,

Figure 2 is a longitudinal view of the threading unit certain partsbeing shown in central vertical section,

Figure 3 is a section through the return drive mechanism but showing thereturn sleeve in an advanced position,

Figure 4 shows the oiling system for the unit,

Figure 5 is a view in partial section of the drive sleeve for rotatingthe tool carrying spindle,

Figure 6 is a view in partial section, broken along its length, of thetool carrying spindle,

Figure 7 is a top plan view of the rear end of the threading unitshowing the limit operated switch means and the connection to a leadcontrol yoke member,

Figure 8 is a side view of the rear end of the threading unit showingthe removable housing for the lead screw and lead nut means,

Figure 9 is a diagram of the trols, and

Figure 10 is a schematic representation showing generally the overallassociation of the mechanical and electrical components of an exemplarythreading unit.

In the exemplary embodiment of the present invention illustrated thereis shown a tool carrying spindle mounted in a compact threading unithaving associated therewith a drive unit for rotating the spindle, areturn unit for returning the spindle after it has completed a threadingoperation and a controllable lead means for advancing the spindle uponits rotation by the drive unit. These components can be coordinatedautomatically or may be subjected to individual manual actuation. Asshown, the spindle carries a collapsible die head.

various electrical con- Referring more particularly to the drawings, inwhich the same reference numerals are used to designate like parts inthe several views, the numeral 10 designates a threading unit embodyingthe present invention carried by any suitable support such as a base ortable 11 for cooperation with a work holding structure 12. The threadingunit 19 includes a housing 13 which supports on its upper surface a maindrive motor 2A which is connected as will be further described forrotation of a tool carrying spindle 16 mounted longitudinally in thehousing 13. A return motor 1A is also mounted on the housing 13 and isconnected to the spindle 16 to return it upon the completion of athreading operation. The spindle 16, as illustrated, supports anautomatically collapsible tap or die head 15. A lead screw 18 is removably mounted on the rear end of the spindle 16 and removable lead nutsegments 19 are carried in the rear end of the housing 13 forcooperation with the lead screw to advance the spindle 16 axially uponits rotation by its drive motor 2A.

The spindle 16 has a tool mounting flange 21 at its outer end, isrotatably and slidably carried in the housing 13, and extendstherethrough. As shown in Figure 6 the spindle unit 16 has portions 22,23 and 24 for the mounting respectively of a drive unit sleeve, a returnsleeve, and a lead screw. Oil grooves 25 are provided in its outersurface for the lubrication of the sleeves.

The lower portion of the unit housing 13 forms an oil reservoir A camdriven lubrication pump 29 is located in this reservoir for supply oflubricating oil through conduit 30 (see Figure 4) and branch 39 to therear bearing 51 and an intermediate portion of the spindle axisrespectively. If desired an additional conduit can be utilized for thelubrication of the lead unit in the rear of the unit housing. An oilretaining ring 14 seals the forward end of the housing 13 relative tothe drive sleeve 36. Oil sealing ring 17 is provided between the drivesleeve 36 and the sliding spindle 16 at their forward ends.

The structure for rotating the tool carrying spindle 16 is more clearlyshown in Figures 2 and 5. The main drive motor 2A drives continuously ina single direction in this embodiment through belts 26, amultiple-sheave 28 in the lower portion of the unit, across under thespindle 16, and to a gear 30, which is the drive gear of a set of changespeed gears 30, 31 and 32. The gear 31 of this set is mounted in abracket 33 to allow adjustments of the gear 31 when different sets ofgears are inserted. These gears are accessible through a removable cover20. Gear 32 drives a worm 34 which engages a worm gear 35 mounted on thedrive sleeve 36 by threaded retaining rings 37 and 38. The drive sleeve36 is rotatably mounted in the threading unit 10 by bearings 40 and 41.The drive sleeve 36 also supports the spindle 16 which is slidablymounted therein. A radial drive pin 43 projects through a slot 42 in thedrive sleeve and is threaded into the spindle at 44 for rotation thereofbut allows axial sliding of the spindle 16 within the drive sleeve 36.The drive sleeve 36 has internal oil grooves 45 and has threadedsections in its outer surface at 46, 47 and 48 for the mounting of thebearing retaining rings 37 and 38 and a retaining ring 49 for the innerrace of the rear bearing 41.

Next situated along the length of the spindle 16 is a return sleeve 50which abuts a bronze washer 59 be tween it and a shoulder on the spindleand which is retained against axial movement relative to the spindle atits inner end by a bearing 51, a sleeve 52, and a retaining ring 53threaded onto the spindle 16 at 54. The sleeve 52 is keyed to thespindle 16 at 55, shown in Figure 6 and cooperates with an oil retainingring 63 mounted in the housing.

The return motor 1A drives through a chain 56 to a sprocket 57 enclosedin a removable housing bolted on the unit and indicated at 58. Thesprocket 57 which is driven continuously in a counter-clockwisedirection as viewed from its left-handface in Figure 3 once the motor 1Ais energized, drives through a controllable planetary clutch unit 60 toa pinion 61 which engages a rack 62 extending along the return sleeve50.

The sprocket 57 is keyed to a shaft 64 which in turn has a driven sungear 65 keyed thereto at its inner extr'emity. Planetary pinions 66 meshwith sun gear 65 and are carried by an annular member 67 which is keyedat 68 to a shaft 69 which extends transversely through the threadingunit. An internal gear 70 meshes with the planetary pinions 66 and ismounted in an annular member 71 journaled about the shaft 64. About thisannular member 71 is a brake band 72 controlled through a member 73actuated by solenoid means referred to later. About the annular member67 which supports the pinions 66 is another brake band 74 controlled bya member 75 which is also solenoid actuated. Upon tightening of brakeband 72 (with band 74 held released) the sun gear 65 will drive theplanetary pinions to planetate them along stationary internal gear 70,.carrying with them the annular member 67 upon which they are mounted,and driving the return sleeve 50 for return of the spindle 16. Whenmember 75 is actuated to close brake band '74 (with band 72 heldreleased allowing annular member 71 to be rotated by pinions 66 withouttransmitting a driving torque) the return pinion 61 and its meshing rack62 are also braked, thereby preventing longitudinal movement of thespindle 16. This latter structure permits vertical mounting of thethreading unit. With both bands released the planetary gear clutch unitis in an idle condition, neither transmitting a drive torque nor brakingthe output shaft. The shaft 69 is mounted in the unit housing 13 bybearings '77 and 78 and has oil retaining rings 79 and 86 adjacent therespective ends thereof. The shaft 69 extends outward through a fitting76 on the housing 13 and has a projection provided at 81 for theinsertion of a handle should it be desired to manually position thespindle 16.

If desired, return could be achieved by leaving the lead nut segmentsengaged and using a reversible main drive motor.

A radial projection 82 is threaded into an enlarged portion 84 of thereturn sleeve 50 and is carried with said sleeve 50 when it is movedwith the spindle upon its threading operation and return. At its outerend projection 82 is inserted into a member having two portions forminglongitudinally extended support elements 86 and 87. These elements 86and 87 are shown in section in Figure 3, in a side view in Figure 2, andin a plan view in Figure 7. Elements 86 and 87 are also carried as thespindle moves axially and the member of which they form the majorportion is mounted for such movement in guide rails 88 and 89 fixed onthe housing wall. Carried on these longitudinal support elements 36 and87 are adjustable limit projections 90 and 91. Knobs 93 and 94 areprovided respectively on limit projections 90 and 91 for manualadjustment of each of these projections upon the longitudinal elements86 and 87 thus con-trolling their association with an electrical circuitswitch means later described in detail. These switch means control thereturn drive brake bands and the actuation of the lead nut segments atthe selected forward and rearward limits of spindle operation.

A lead screw 18 is mounted on the inner end of the spindle 16, is keyedthereto by a key seated in the spindle at 96 (see Figure 6) and isretained on the spindle by a retaining ring 97. At its forward end screw18 abuts a washer 92 which contacts an abutment on the spindle. A leadnut mounting component 98 is fixed to the unit wall at 9 9. Radiallymounted in this component 98 for engagement with the lead screw 18 arelead nut segments' 19 preferably three in number. Radially situatedsprings 100 engage pins 101 in each of the lead nut segments urging thesegments radially outward. Axiall'y slidable on the component 98 is alead nut control sleeve 102 urged axially outwardly in the exemplaryembodiment illustrated by springs shown at 104. This lead nut controlsleeve 162 has a cam 105 on its inner surface. This sleeve is moved toengage and disengage the lead nut segments 19 with the lead screw 18 andis actuated by a yoke member 106 which has projections seated therein at163. The yoke 106 is pivoted about a fixed point 128 (see Figure 10). Itwill be apparent that the yoke 106 could be easily adapted for manualactuation if desired.

A general association of the yoke control is shown in Figure 7. Rollers167 and 1138 are mounted on the switch units 109 and 116 for engagementwith the respective limit projections 96 and 91 at the adjusted extremesof desired spindle movement. Roller 107, which is actuated by theforward limit, controls through a switch unit 169 a pull solenoid shownat 5A. Roller 198 actuates a double throw switch 110 to energize pushsolenoid 3A. The details of the electrical circuits are later explainedin connection with Figure 9. Solenoids 3A and 5A have armatures whichare connected together and to a bar 113. This bar 113 is connected to ayieldable connection 114 fastened to one end of the yoke 106. Connection114 will allow positive actuation of the yoke 196 to move the sleeve 102to the left as viewed in Figure 7 and allow radial projection of thesegments 19 by the springs 160 to disengage the segments from the leadscrew 18. When the push solenoid 3A is engaged the yieldable connection114 allows a limited pro-loading in order to prevent forceful engagementof the lead nut segments 19 with the lead screw 13 by the inner camsurface 105 before the nut and screw elements are properly aligned.

In Figure 8 is shown the removable housing sections for the lead unit.With the components of the lead control unit located at the rear end ofthe threading unit 10 they are readily accessible by removing the uppercomponent 116 of the removable housing. After removing the uppercomponent 116 the retaining ring 97 can be unscrewed annd removed, thespindle advanced, and the lead screw and lead nut segments can be easilyremoved and replaced. This structure allows the insertion of cooperatingpairs of lead screws and lead nuts to obtain various leads as desired.

In Figure 10 is shown a schematic arrangement of the major components ofthe threading unit and their association relative to the spindle 16 whenit is at its rearward position as shown in that figure. The spindle 16has a tool holding flange 21 at its outer extremity and spaced along itsaxis, in order, the drive sleeve 36, the return sleeve 50, the lead unit102 supporting the lead nut segments and the lead screw 18. Theplanetary gear clutch unit is shown at 68. Mounted on top of this unitare solenoids 6A, 4A (see Figure 10) which are onclosed in a housingshown in Figures 1 and 2. Solenoid 6A is attached to member 73 in Figure3 and actuates the return brake 72. Solenoid 4A is attached to member 75of Figure 3 and actuates the brake 74 which prevents spindle movement.Solenoid 6A is a pull solenoid and closes brake 72 which is normallybiased in a releasing position. Solenoid 4A is also a pull solenoid andwhen energized releases brake 74 which is normally spring biased closed.Yoke 106 which actuates the lead nut segments 19 is pivoted at its upperend 128 and has a projection 129 which cooperates with a switch 120.

Figure 9 shows the electrical circuit embodying the various controls forthe threading unit. Power is supplied through connections 131. Relays inthe secondary transformer circuit control switches in that circuit andalso actuate switches situated to control components energized from themain line. The relays are numbered 1 through 6 and the switches actuatedthereby are correspondingly numbered with small letter subscripts.

The operation of the threading unit is set forth below with particularreference to Figure 9 which shows the wiring circuit above referred towhen the spindle is in its rear position and Figure 10 which shows theassociation of the various components.

The master stop switch 122 is normally closed, as shown. Closing thestart switch 121 for the return motor 1A energizes relay 1 to closeswitches 1a and 11), starting the return motor 1A and setting up thecircuit for the other controls. Stop switch 124 is normally closed andrear limit contacts 110a are closed by double throw switch 110 when thespindle occupies its rear position at the start of a threadingoperation. Accordingly when main drive motor start switch 123 is closedrelay 2 is energized to close switch 2a, starting the drive motor 2A.Switch 2b in the secondary circuit is also closed to set up the circuitto relays 2 and 3 around contacts 110a and 123. Thus upon engagement ofcycle start switch 125, relay 3 is energized through normally closedswitch d to close switch 3:: thus energizing push solenoid 3A to closethe lead sleeve and engage the lead nut segments. Switch 3b is closedaround the cycle start switch 125. Switch 3c is also closed to energizerelay 4, closing switch 4a, and energizing solenoid 4A to release brake74. This causes the spindle to advance on a threading operation. The diehead 15, illustrated for purposes of example only, has abutment meanslocated on a rod 112 to coordinate its actuation with spindle advanceand return through the operating yoke 115.

When the limit projection 90 contacts the roller 107 at the adjustedforward limit of spindle travel it engages and closes switch 109 whichis normally open. Lower contacts 110!) are closed (and upper contacts110a are opened) when the rear limit projection 91 releases the switch110 upon movement of the spindle from its rear position. Closing switch109 accordingly energizes relay 5, closing switch 5a to energize pullsolenoid 5A, opening the lead sleeve. Relay 5 also opens switch 5d thusde-energizing relay 3 to de-energize push solenoid 3A. Relay 5 alsocloses switch 5b to keep relay 4- energized and the brake 74 released.Switch 50 is also closed when relay 5 is energized to furnish current torelay 5 When switch 109 is released. When pull solenoid 5A is energizedto actuate the yoke 105 for disengaging the lead nut segments theprojection 129 thereon engages switch 120, closing same, to energizerelay 6 which in turn closes switch 6a to energize solenoid 6A. Solenoid6A closes brake 72 and returns the spindle. This se quence of returnoperations is necessary in order to prevent return movement of thespindle before the lead nut segments are fully disengaged. Solenoid 4Ais held energized through switch 5b controlled by relay 5 thus holdingthe brake 74 released.

When the rear limit projection 91 contacts roller 108 switch 110 closesupper contacts 110a and opens lower contacts 11017 thereby de-energizingsolenoids 6A, 5A and 4A. The spring associated with solenoid 4A closesthe brake 74 and holds the spindle against axial movement.

If power should fail at any time during the stroke of the spindle thesolenoid 4A will release its spring loaded brake 74 which will engageand hold the spindle in the position it occupies at the time of powerfailure.

If in the forward stroke trouble should develop and the operator desiresto stop forward motion of the spindle, he would push stop button 122.This would shut oft all current and the spindle would be held inposition by the spring loaded brake 74. To then return the spindle toits back position, start button 121 would be depressed to start thereturn motor 1A. If the tool is in cutting position it must be releasedfrom the work. The emergency return button 126 is then pushed energizingsolenoids 6A and 5A, returning the spindle to its starting position. Themain drive motor 2A can only be started when the rear limit projection91 is engaging the roller 108, closing upper contacts a.

It is thus seen that a threading unit has been provided which is simpleand compact in arrangement, that the various components thereof and inparticular the lead screw and lead nut unit are readily accessible andcan be easily removed and replaced. The association of the lead screwdirectly on the tool holding spindle with the engageablo lead nutsegments gives an extremely accurate and positive advance control in acomparatively simple construction. This direct control of lead by meansof a lead screw mounted on the tool holding spindle avoids the errorsassociated with an intermediate gear drive or the like resulting fromlost motion in the gears and errors in their configuration. The locationof the lead screw at the rear end of the spindle and the lead nutsegments at the rear of the unit housing makes it relatively easy toremove and insert lead screws and lead nut segments for particularoperations. The lead nut segments are held positively engaged when thecontrol sleeve is moved to engage them; however, the sleeve is actuatedthrough a yielding pressure to prevent forceful engagement before thelead screw and lead nut segments are properly aligned. A circuit hasbeen provided to give full automatic actuation of the threadingoperation and provision has been made for emergency conditions. The unitcan also be readily adapted for manual actuation of the return and leadunit components.

While the form of apparatus herein described constitutes a preferredembodiment of the invention, it is to be understood that the inventionis not limited to this precise form of apparatus, and that changes maybe made therein without departing from the scope of the invention whichis defined in the appended claims.

What is claimed is:

1. A threading machine comprising a threading unit and a workpieceholder, said threading unit comprising a tool holding spindle, meansslidably and rotatably supporting said spindle in said threading unit, aholder for a collapsible cutting head fixed to the outer end of saidspindle, a driving sleeve fitted coaxially about said spindle adjacentsaid cutting head holder, means connecting said drive sleeve to saidspindle for rotation thereof but allowing relative sliding therebetween,a power drive means including change speed gearing connected to rotatesaid drive sleeve, a return sleeve coaxially mounted about said spindleadjacent said drive sleeve, abutment means on said spindle at each endof said return sleeve allowing relative rotation of the return sleevewith respect to said spindle but preventing axial movement between theseunits, a rack extending axially along one side of said return sleeve, adrive pinion engaging said rack, return power means drivingly connectedto said pinion, a lead screw mounted on the inner end of said spindleand removably fixed thereto, lead nut segments about said lead screw,means mounting said lead nut segments in said unit in removablerelationship thereto and for movement toward and from said lead screw,resilient means urging said lead nut segments radially outward from saidlead screw, an annular cam means about the radially outward portions ofsaid lead nut segments for positively engaging said lead nut segmentswith said lead screw, adjustable limit projections carried by saidreturn sleeve as it moves axially with said spindle during a threadingoperation, control means for moving said cam means to release said leadnut segments and actuating said return means, in that sequence, after athreading operation, switch means actuated by said adjustable limitprojections and connected to said control means for energization thereofat the selected limits of spindle travel determined by said adjustablelimit projections.

2. A threading unit for use with a workpiece holder comprising a toolholding spindle, means on said spindle for-detachably connecting acollapsible threading tool,

supporting means for rotatably and slidably carrying said spindle insaid threading unit, a drive unit for rotating said spindle in onedirection operatively connected thereto, controllable lead meansoperatvely connected to said spindle, return means having an outputdrive shaft operatively connected to said spindle, control meansconnected. to said return means including means to actuate said returnmeans for return drive, means to place said return means in an idlecondition and means to brake the output shaft thereof, forward andrearward limit means mounted on said threading unit operativelyconnected to said spindle and connected to said controllable lead means.and to said return control means, manually operable cycle starting meansto activate said lead means and place said return means in an idlecondition, means actuated by said forward limit means toplace the leadmeans in inactive position and actuate the return means, in thatsequence, and means actuated by said rear limit means for deactivatingthe return means and braking the return output shaft.

3. A threading unit for use with a workpiece holder comprising ahousing, a tool holding spindle for a collapsible cutting tool, means insaid housing carrying said spindle for rotation and for axial movement,drive means for said spindle mounted in a fixed position relative tosaid housing including a drive connection to said spindle forunidirectional rotation thereof but allowing axial movement of thespindle relative thereto, return power means in said housing for rapidaxial movement of said spindle during its continued rotation in said onedirection, a lead screw fixed to said spindle, lead nut segments spacedabout said spindle and carried for movement inward to engage said leadscrew and control advance of said spindle and outward to clear the leadscrew, actuating means for controlling movement of said lead nutsegments, means connected to said actuating means for releasing saidlead nut segments from said lead screw upon completion of a threadingoperation, and means 'connected to said return means operative uponrelease of said segments to then energize said return power means torapidly return said spindle by axial sliding.

4. A threading unit for use with a workpiece holder and in which arotatable spindle has a precise uniform increment of advance for eachspindle rotation, comprising a spindle, means on said spindle fordetachably connecting a collapsible threading tool, supporting meanscarrying said spindle for rotation and axial movement in said unit,drive means on said supporting means operatively connected to saidspindle for unidirectional rotation of said spindle, a lead unitincluding a lead screw fixed to said spindle and releasable lead nutmeans fixed against rotation on said supporting means for advancing saidspindle upon its rotation by said drive unit, power means for applyingan axial return force to said spindle, limit means responsive to apredetermined axial position of said spindle and operatively connectedto said lead unit for releasing said lead nut means and disabling saidlead unit upon completion of a threading operation, and means connectedto said power means operative upon release of said lead nut means tothen initiate the application of force to said spindle for rapid returnby axial sliding.

5. A threading unit for use with a workpiece holder and in which arotatable spindle has a precise uniform increment of advance for eachspindle rotation, comprising a spindle, means on said spindle fordetachably connecting a collapsible threading tool, supporting meanscarrying said spindle for rotation and axial movement in said unit,change speed drive means on said supporting means operatively connectedto said spindle for unidirectional rotation of said spindle whileallowing axial movement of the spindle relative thereto, a lead screwfixed to said spindle, lead nut segments supported against rotation insaid unit and engageable with said lead screw, a. sleeve coaxial withsaid lead screw and operatively connected to said lead nut segments forengaging and disengaging said segments upon axial movement of thesleeve, power means for applying an axial return force to said spindle,limit means in said threading unit and operatively connected to saidspindle, means responsive to said limit means to axially movesaid sleeveto disengage said segments from said lead screw upon completion of athreading operation, and control means connected to said power meansoperative upon movement of said sleeve and release of said nut segmentsto then initiate application of force to said spindle for rapid returnby axial sliding during continued rotation in the one direction. 7 p

6. A threading unit for use with a workpiece holder and in which arotatable spindle has a precise uniform increment of advance for eachspindle rotation, comprising a spindle, means on said spindle fordetachably connecting a collapsible threading tool, means carrying saidspindle for rotation and axial sliding movement in said unit, drivemeans on said supporting means operatively connected to said spindle forunidirectional rotation of said spindle, a lead unit carried in saidthreading unit at the inner end of said spindle, arranged concentricallywith said spindle and operatively connected therewith for advancing saidspindle upon its rotation by said drive unit, means to control theoperative connection of said lead unit with said spindle including amovable control member, power means for applying an axial return forceto said spindle, adjustable limit means mounted on said threading unitand operatively connected to said spindle,

means connecting said adjustable limit means to said lead unit controlmember for actuation thereof at the adjusted threading limit, andcontrol means actuated by said member after the lead unit is disabled tothen initiate the application of force to said spindle for rapid returnof said spindle by axial sliding during its continued rotation in saidone direction.

7. A threading unit for use with a workpiece holder and in which arotatable spindle has a precise uniform increment of advance for eachspindle rotation, comprising a spindle, means on said spindle fordetachably connecting a collapsible threading tool, supporting meanscarrying said spindle for unit, drive means on said supporting meansoperatively connected to said spindle said spindle, a lead unit foradvancing said spindle upon rotation thereof, said lead unit comprisinga lead screw fixed to said spindle, lead nut segments fixed againstrotation on said supporting means, means mounting said segments in saidthreading unit for movement toward and from said lead screw, resilientmeans in said unit and connected to said lead nut segments urging saidsegments away from said lead screw, cam means operatively connected tosaid lead nut segments for positively engaging said segments with forapplying an axial return force to said spindle, limit means responsiveto a predeterminedaxial position of said spindle and operativelyconnected to said cam means for actuation thereof to release saidsegments and disable said lead unit upon completion of a threadingoperation, and means connected to said power means opera tive uponrelease of said lead nut segments to then initiate application of forceto said spindle for rapid return by axial sliding.

8. A threading unit for use with a workpiece holder and in which arotatable spindle has a precise uniform increment of advance for eachspindle rotation, comprising a spindle, means on said spindle fordetachably connecting a collapsible threading tool, supporting meanscarrying said spindle for rotation and axial movement in said unit,drive means on said supporting means operatively connected to saidspindle for unidirectional rotation of said spindle, a lead unitoperatively connected to said spindle for advancing said spindle uponits rotation by said drive unit, said lead unit comprising a lead screwrotation and axial sliding in said for unidirectional rotation of a saidlead screw, power means fixed to said spindle at one end thereof, aplurality of lead nut segments for threaded engagement with said leadscrew, means mounting said lead nut segments in said threading unitspaced about said lead screw, fixed against rotation and carried formovement toward and from the screw, resilient means in said threadingunit connected to said lead nut segments urging said segments away fromthreaded engagement with said lead screw, a sleeve movable along theaxis of said spindle and having cam means on its inner surface incontact with outer portions of said segments for positive engagement ofsaid segments with said lead screw upon axial movement of said sleeve inone direction, power means for applying an axial return force to saidspindle, limit means responsive to a predetermined axial position ofsaid spindle and operatively connected to said sleeve for movementthereof in the other direction for releasing said segments and disablingsaid lead unit upon completion of a threading operation, and meansconnected to said power means operative upon releasing movement of saidsleeve and retraction of said segments from threaded engagement withsaid screw to then initiate application of force to said spindle forrapid return by axial sliding.

9. A threading unit for use with a workpiece holder and in which arotatable spindle has a precise uniform increment of advance for eachspindle rotation comprising a tool holding spindle for a collapsiblecutting tool, supporting means carrying said spindle for rotation andaxial movement in said unit, drive means operatively connected to saidspindle for unidirectional rotation thereof, a lead unit for advancingsaid spindle upon spindle rotation, said lead unit comprising a leadscrew carried coaxially with said spindle, lead nut means, meansmounting said lead nut means in said threading unit for disengagementand engagement with said lead screw, means operatively connected to saidlead nut means for control thereof, power means for applying an axialreturn force to said spindle, means for actuating said power means forreturn of said spindle, forward limit means mounted on said threadingunit and operatively connected to said spindle, means actuated by saidforward limit means and connected to said lead nut control means todisengage said lead nut means and means responsive to disengagement ofsaid lead nut means to energize said power actuating means to theninitiate application of force to said spindle for rapid return by axialsliding, whereby sequential disengagement of said lead nut means andactivation of said return power means is achieved in that order.

10. A threading unit for use with a workpiece holder and in which arotatable spindle has a precise uniform increment of advance for eachspindle rotation, comprising a spindle, means on said spindle fordetachably connecting a collapsible threading tool, supporting means forrotatably and slidably carrying said spindle in said threading unit, adrive unit for rotating said spindle operatively connected thereto, alead unit for advancing said spindle upon rotation thereof, said leadunit comprising a lead screw operatively connected to said spindle, alead nut segment, means mounting said segment in the threading unit formovement toward and from said lead screw, resilient means mounted insaid threading unit and connected to said lead nut segment for urgingsaid segment away from said lead screw, cam means operatively connectedto said lead nut segment for positively engaging said segment with saidlead screw, a control connection to said cam means including opposingabutment means, resilient means between said abutment means providing alimited amount of yielding therebetween, whereby said resilient meansyields when said connection is moved to initially engage said lead nutsegment with said lead screw, following which the abutment means engageand the cam means is positively actuated for positive engagement, andmeans to disengage said lead nut segment from said lead screw andthereafter return said spindle.

11. A threading unit for use with a workpiece holder and in which arotatable spindle has a precise uniform increment of advance for eachspindle rotation, comprising a spindle for a collapsible tool,supporting means carrying said spindle for rotation and axial movementin said unit, drive means operatively connected to said spindle forunidirectional rotation thereof at variable speeds, a lead screw fixedto said spindle, a lead nut segment, means mounting said segmentsubstantially radially with respect to said spindle for movement towardand from said lead screw for controlled advance thereof upon lead screwrotation, resilient means in said unit operatively connected to saidsegment urging said segment away from said screw, an axially movablesleeve having cam means on its inner surface in contact with an outerportion of said segment, a control connection to said sleeve having aspring means therein for yieldingly moving said sleeve to engage saidsegment with said screw, return power means for applying an axial returnforce to said spindle, limit switches operatively connected to saidspindle, electrical actuating means connected to said control connectionand said limit switches to move said sleeve and release said segment ata predetermined spindle position, and means connected to said returnpower means operative upon disengagement of said segment from said leadscrew to then initiate application of force to said spindle for rapidreturn by axial sliding.

References Cited in the file of this patent UNITED STATES PATENTS 92,682Whipple July 13, 1869 1,666,732 Brophy Apr. 17, 1928 2,501,298 WinchellMar. 21, 1950 2,551,517 Webb May 1, 1951 2,581,082 Drissner et al Jan.1, 1952 2,622,252 Wernli Dec. 23, 1952 2,637,052 Woock May 5, 19532,660,738 Hieber Dec. 1, 1953

